Pressure swing adsorption (PSA) is a well-known method for the separation of bulk gas mixtures and for the purification of gas streams containing low concentrations of undesirable components. The method has been developed and adapted for a wide range of feed gases, operating conditions, product purity, and product recovery. Many pressure swing adsorption systems utilize two or more parallel adsorbent beds operated in a cyclic sequence in order to maintain a constant product flow rate while selected beds undergo various steps including adsorption/make product, depressurization, evacuation, purge, pressure equalization, repressurization, and other related steps. Multiple adsorbent beds using numerous process steps are required to achieve high purity and/or recovery of valuable gaseous products such as hydrogen, carbon oxides, synthesis gas, light hydrocarbons, and the like. Multiple-bed PSA systems using these process steps also are applied in the recovery of oxygen from air for various industrial applications and for portable medical oxygen concentrators.
The proper selection and design of the adsorber vessels and beds is an important factor in minimizing capital cost and maximizing operating efficiency of PSA systems. Various types of designs have been used in the art to effect proper gas-adsorbent contact during the process steps, and most are designed for installation within cylindrical pressure vessels. Granular adsorbents are widely used and can be installed in cylindrical beds in which gas flows in the axial direction or in annular beds in which gas flows in the radial direction. Various methods have been used to support the beds of granular adsorbent in axial or radial flow configurations.
There is a continuing need in the adsorptive gas separation art for vessel designs that maximize the amount of fabrication work carried out in the shop and minimize the amount of fabrication and assembly work required during field installation. This requires adsorber vessels that can be shipped safely in nearly-complete form, preferably wherein the vessels are packed with adsorbent in the shop. There also is a need for bed designs that minimize the void volume (i.e., the empty volume not occupied by adsorbent) within adsorber vessels. Further, it is desirable to use adsorber designs and fabrication methods that ensure substantially identical performance of each adsorber bed in the operation of multiple-bed PSA systems. In addition, there is a need for improved design and operating methods for large PSA plants with gas production rates greater than the capacity of single-train systems that use adsorber vessels having the maximum shippable diameter.
These needs are addressed by the embodiments of the invention described below and defined by the claims that follow.